We Run Over All The Alternative Auto Fuels

Over the last few years, there has been a general move to find cleaner, more energy efficient fuels to run our vehicles. Although alternative energy such as ethanol, Liquid Petroleum Gas (LPG) or biodiesel may not be as widespread as petrol or diesel, they are becoming more and more common, and are generally much cheaper. Not only that, but energy efficient cars and those with low emissions can also qualify for a range of discounts.


The four major alcohols that have been considered of interest as alternative fuels are methanol, ethanol, propanol and butanol. All four of these alcohols may be synthesised biologically (termed bioalcohols), and have characteristics which enable them to be used in vehicle engines. They can offer a range of environmental benefits: they are biodegradable, renewable, produce less local air pollutants than fossil fuels and reduce tailpipe emissions of many pollutants.


Bioethanol is a high octane liquid fuel made from plant material and can be used as a substitute for use in petrol engines or as a petrol additive. It is currently the world’s main biofuel, and is used in countries such as Brazil, Sweden, Pakistan, India, China, Thailand and Japan. It can be produced from crops such as oilseeds, sugar beet, sugarcane and corn (maize), and in the future it may also be possible to produce it economically from straw, wood and even household waste.

When used as a blend of 5% with petrol, bioethanol may be used in cars without any need for engine modification. However, a number of manufacturers (for example, Ford and Saab) have produced flexible fuel vehicles that can run on either E85 bioethanol blend (a blend of 85% ethanol and 15% petrol) or normal petrol in the same fuel tank in any mix.

However, high concentrations of ethanol may degrade some plastic or rubber parts of fuel delivery systems, particularly in older cars, and has 37% less energy per litre than petrol.


Whilst methanol may be obtained from natural gas or petroleum, it may also be acquired from agricultural biological waste, such as from wood, coal or eucalyptus. Methanol is almost always used as an additive to petrol engines, rather than on its own. However, the Indy Racing League used pure methanol from 1965 up until 2006, switching to an all-ethanol mix in 2007.

Methanol is even more corrosive than ethanol, and is highly toxic; extensive exposure to it could lead to permanent health damage, including blindness. It is also volatile, which could increase the risk of fires and explosions compared to ethanol. An additional problem of methanol is that its energy content is only 45% that of petrol, and 75% of ethanol. (Petrol = 30 megajoules/litre, ethanol = 22 megajoules/litre, methanol = 16 megajoules/litre).

Propanol and Butanol

Propanol and butanol have also been considered for use as alternative fuels; however, although they are considerably less toxic and less volatile than methanol, the fermentation process used to extract them from cellulose is relatively difficult to carry out. The conversion also produces an extremely unpleasant smell, a factor which must be taken into consideration when designing and locating a fermentation plant.


Biodiesel is a processed fuel derived from biological sources that can be readily used in diesel-engined vehicles. It is produced by chemically treating waste or virgin pressed vegetable oils, such as oilseed rape or soybean oil. Although biodiesel is not necessarily a very clean burning fuel, it is made from a renewable source.

Bio-diesel can be used as a 5% blend with ultra-low sulphur diesel (ULSDF) in any diesel vehicle without affecting engine warranties. Although many modern diesel engines can run on pure biodiesel, few vehicles are actually warranted to use it as such, so check with your manufacturer before using. Since biodiesel acts as a solvent it can degrade rubber parts in vehicles built before 1990. However, modern rubber replacements are nor affected.

Biodiesel actually cleans the engine, and so fuel filters may become clogged with particulates if a quick transition to pure biodiesel is made from fossil diesel. It is therefore suggested biodiesel is gradually phased into the fuel supply of vehicles that have previously run on fossil diesel, and that the fuel filter is changed within 600-800 miles.

In severe winter conditions pure biodiesel may become waxy, making it difficult to start the engine; however, the use of additives or the addition of standard diesel to the blend can combat this problem.


  • Is produced from renewable energy sources
  • Is biodegradeble and non-toxic
  • Produces a net carbon dioxide emission into the atmosphere 78% lower than non biofuels
  • Produces less particulate emissions compared to conventional diesel engines
  • Is usually cheaper than standard diesel
  • Produces more nitrogen oxide NOx tailpipe-emissions than standard diesel
  • May start to gel at low temperatures
  • May degrade rubber parts in vehicles built before 1990


Biofuel is any type of fuel that has been derived from biomass (recently living organisms or their by-products), such as crops, waste food and manure. Unlike other natural resources such as petroleum, coal and nuclear fuels, biofuel is a renewable energy source. Example include biodiesel, bioethanol and biobutanol.

Biofuel may be obtained from the by-products of other industrial, agricultural or household processes, such as straw, timber, waste vegetable oil, manure, sewage, rice husks, biodegradable waste and food leftovers. It may also be acquired from specifically grown products, such as flaxseed and rapeseed (Europe), maize and soybeans (North America), palm oil (South-East Asia) and sugar cane (Brazil).

In general, biofuels are blended in with traditional fossil fuels in small amounts – usually about 5-20%. This requires no modification to the vehicle’s engine. However, in warm climates, straight vegetable oil may be used in some older diesel engines, whilst bioethanol is commonly used in high percentages (up to 100%) in modified engines in Brazil, Argentina and Sweden.

Compressed Natural Gas (CNG)

Compressed Natural Gas (CNG) can be used as a substitute for petrol or diesel fuel and is seen as a environmentally clean alternative to fossil fuels. CNG powered vehicles are more fuel efficient, emit fewer toxic chemicals and operate more quietly than conventional cars.

Made by compressing purified natural gas, CNG (not to be confused with LNG – Liquefied Natural Gas) is one of the major fuel sources for cars in Pakistan, Bangladesh, India, Argentina and Brazil. Many petrol and diesel engines can be converted to run on CNG.


Electric cars may be powered in a number of ways:

from chemical energy stored in on-board batteries (battery electric vehicle or BEV)
from both an on-board rechargeable energy storage system (RESS) and a fueled propulsion power source (hybrid vehicle)
generated on-board using a fuel cell (fuel cell vehicle)
Battery electric vehicles are usually charged overnight, although most will recharge fully in about an hour or less. The distance the car can travel on a single charge will depend on the number and type of batteries used, and the weight and type of vehicle. However, in general, lead-acid batteries have a range of 20 to 80 miles per charge, NiMH batteries have higher energy density and may deliver up to 120 miles, whilst new lithium-ion batteries can provide 250-300 miles of range per charge.

Electric vehicles are generally much quieter than internal combustion vehicles, alleviating noise pollution. They also produce zero-emissions at the vehicle tailpipe. However, it must be remembered that recharging a battery takes energy from the electricity grid, which often relies on nuclear-powered and fossil-fuelled power plants.

Fuel Cells

Fuel cells produce electricity from an external supply of oxygen and fuel such as petrol, methanol, hydrogen or natural gases, and then use this electricity to power a car. Fuel cells are much more efficient than combustion engines, and as they do not contain any major moving parts, they are also extremely reliable.

Hydrogen fuel cells have the benefit of zero-point of use emissions. However, the production of hydrogen requires electricity in itself, which is taken from power plants that do produce emissions.

It is hoped in the future that a hydrogen fuel cell vehicle will be about 100% more efficient as a similarly sized conventional petrol vehicle, and up to 50% more efficient than a hybrid vehicle.

Hybrid Cars

Hybrid vehicles are those that use two fuel sources for energy; an on-board rechargeable energy storage system (RESS) and a fuelled power source. The majority of hybrid cars are petroleum-electric hybrid vehicles (also called Hybrid-electric vehicles or HEV), which use internal combustion engines and electric batteries to power electric motors.

Nearly all hybrids use petrol or diesel as their fuel source, although other fuels such as biobutanol, bioethanol or other biofuels may also be used. A number of other hybrid vehicles use hydrogen fuel.

Vehicles can prolong the charge on their batteries by capturing energy via regenerative braking (i.e. storing some of the kinetic energy that would otherwise be lost to heat when braking).


Vehicles can be powered by hydrogen in one of two ways: combustion or fuel-cell conversion. In combustion, the hydrogen is ‘burned’ in engines in essentially the same method as traditional petrol cars. In fuel-cell conversion, the hydrogen is turned into electricity through fuel cells which then power electric motors.

Hydrogen can be obtained from various products, including natural gas (methane), coal, liquefied petroleum gas or by splitting water (H20) into oxygen and hydrogen (known as thermolysis). When the hydrogen is burned, it obtains oxygen from the air and produces heat and water vapour, making it the cleanest burning of all the alternative fuels.

The internal combustion hydrogen car has more power and is faster than hydrogen fuel cell electric cars. However, the use of this technology is still in the experimental stage; at the moment, a full tank of hydrogen, in the gaseous state, would last only a few miles before the tank became empty. However, methods are being developed to reduce tank space, such as using liquid hydrogen or by using metal hydrides in the tank.

Many companies are currently researching and developing hydrogen internal combustion engine cars, for example BMW, who has built two models that use liquid hydrogen; the 750hL and the BMW H2R, which broke the speed record for hydrogen cars at 186 mph. Other companies such as General Motors Corp and DaimlerChrysler, are investing in the slower, weaker, but more efficient hydrogen fuel cells instead.

Liquefied Natural Gas (LNG)

Liquefied natural gas (or LNG) is natural gas that has been processed to remove impurities and heavy hydrocarbons and then condensed into a liquid. It has a fraction of the volume of standard natural gas, making it much more cost-efficient to transport over long distances. LNG should not be confused with LPG – Liquid Petroleum Gas.

LNG offers an energy density comparable to petrol and diesel fuels and produces less pollution. However, it must be stored at extremely low temperatures to keep it in its liquid state, making it expensive to store.

Liquid Petroleum Gas (LPG)

LPG, or Liquefied Petroleum Gas, is a mixture of hydrocarbon gases manufactured during the refining of crude oil, or extracted from oil or gas streams as they emerge from the ground. Also known as Autogas, LPG is widely used as an environmentally friendly automotive fuel, as it produces significantly less emissions than petrol (including carbon monoxide, carbon dioxide, hydrocarbons and oxides of nitrogen). LPG also emits 90% less particulates, in weight, than diesel engines.

In the UK, autogas consists principally of propane, and is the third most-used fuel after petrol and diesel. The Government has offered a range of incentives to encourage motorists to convert to LPG, including lower vehicle excise duty (road tax) and company car tax. LPG is also relatively inexpensive to buy (about half the price of petrol), as it attracts a lower fuel duty. However, this cheaper price is off-set slightly by the fact that cars achieve 80% fewer miles per gallon with LPG than they would with petrol or diesel.

Most cars powered by LPG iare hybrid vehicles, with tanks for both LPG and petrol. These vehicles are designed to start up using the petrol system, after which the gas system cuts in and takes over. There are a number of these hybrid cars available commercially available, including the Volvo S80, the Vauxhall Corsa and the Mitsubishi Shogun, amongst many others. The majority of standard petrol vehicles can also be converted to use LPG for around $2000; a second independent fuel system with its own tank is added to the car, often in place of the spare wheel or underneath the vehicle.

Solar Power

A solar car is an electric vehicle powered by energy obtained from solar panels (also known as photovoltaic cells) fixed on the car. However, although the idea of a solar powered car is an attractive one (no fuel to buy and no emissions), solar cells generally produce too little power to run a full-sized electric car, producing only about 1,500 watts, which is enough to power a hairdryer. Although the cells can be used to run prototype cars, these vehicles are usually are extremely light (approximately 180 kg) and would not be strong enough to protect a driver in an accident with another vehicle.

Although solar cars are not currently a practical form of transportation, they are often raced in competitions, such as the World Solar Challenge – a 3,021 km race across the centre of Australia from Darwin to Adelaide. Competitors include entries from universities keen to develop their students’ technological and engineering skills, along with professional teams such as Honda and GM.